A heat exchanger is a device built for efficient heat transfer from one medium to another, whether the media are separated by a solid wall so that they never mix, or the media are in direct contact. They are widely used in Space Heating, Refrigeration, Air Conditioning, Power Plants, Chemical Plants, Petro-chemical Plants, Petroleum Refineries, and Natural Gas Processing. One common example of a heat exchanger is the Radiator in a car.
The mechanical design of a heat exchanger depends on the operating pressure and temperature .
In Direct Contact type of heat Exchanger heat is directly transferred between Hot and Cold fluids.
There is no separating wall between the hot and cold fluids.
Most direct contact heat exchangers fall under the Gas- Liquid category, where heat is transferred between a gas and liquid in the form of drops, films or sprays.
Properties of both fluids, such as viscosity, thermal conductivity, density, specific heat and reaction on the metal in contact are essential to determine the pumping, thermal requirement and material construction.
In an Indirect Contact Type Heat Exchanger, the fluid stream remains separated. There is separating wall between the hot and cold fluids.
The heat transfer in this type of heat exchanger takes place continuously through a dividing wall.
Most indirect contact heat exchangers fall under those gases and liquids that are soluble in nature.
Difference between Direct and Indirect Heat Exchanger Direct Heat Exchanger Indirect Heat Exchanger Not have a separating wall between two fluids. Have a separating wall between two fluids. Mostly used for those gases and liquids that are not soluble in nature Used for those gases and liquids that are soluble in nature. Mostly use drops and steam for heat transfer There is no use of steam and drops
This type of heat exchanger are categorized in following types:-
Double Pipes heat Exchange
Shell & Tube Heat Exchanger
Spiral Heat Exchanger
Cracked Surface Heat Exchanger
Shell and Tube Heat Exchanger Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contains the fluid that must be either heated or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. A set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned.
Plate Heat Exchanger Plate heat exchanger uses plates to exchange the heat. This the most common and popular method that is used in most common devices to keep the device cool.
Jacketed & Kettle Heat Exchanger In this type of heat exchanger, the liquid to be heated is contained in a vessel with an agitator to stir the liquid across the heat transfer surface .It is a batch type equipment. Steam or hot water may be used as heating medium. Generally, steam is allowed to condense in the jacket. Care is to be taken so that there is minimum incorporation of air with the steam and that steam should not be in super heated state. When heating is done by hot water, it can either be spread on the outer surface of the hemispherical container or flooded into the heating/ cooling medium passage. The former method is more efficient, as the transfer of heat is faster due to rapid moving thin film or heating medium.